In recent years, solid-state light sources and other narrow-wavelength-band and/or polarized light sources capable of producing visible light have drawn significant attention as alternative light sources to traditional light sources for use in imaging systems (such as projection systems) due to many advantages, such as compact size, greater durability, longer operating life, and lower power consumption. For example, solid state sources such as LASERs, light-emitting-diodes (LEDs), and pumped non-linear optical crystals are increasingly used in imaging systems, especially imaging systems that employ one or more light valves each of which comprises an array of individually addressable pixels.
Despite their recognized superior properties over traditional light sources, solid-state light sources can be difficult to optically couple with light valves in imaging systems for illuminating light valves. For example, it is difficult to generate a far-field illumination area with uniform illumination intensity at a light valve location using solid-state or narrow-band light sources. This arises from a fact that the illumination light from the solid-state sources can be distributed over a large solid angle, up to a full hemisphere.
In color imaging applications using solid-state sources (or other narrow-band sources), light sources comprising one or more solid state sources emitting light of different colors or spectral profiles are provided to illuminate light valves. It is desired that the light of different colors illuminates a light valve along substantially the same optical path, for instance, with substantially the same incident angle to the pixels of the light valve. It is desirable that the multiple beams, such as colored beams, overlap to occupy the same angular and spatial optical phase space.
Because a single light source may have limited output power, which may not be sufficient to generate images with satisfactory brightness, multiple light sources for the same color light (with the same wavelength or different wavelengths, and with the same or different electromagnetic polarization state) can be employed in an imaging system. Regardless of different spatial arrangements, the light beams from separate light sources are spatially separated when exiting from the light sources. Without proper management, the spatially separated light beams may result in distorted illumination field, as well as other unwanted optical effects at the light valve, such as poor image uniformity and reduced system brightness.
Therefore, what is desired is an optical system that is capable of directing light from light sources to one or more light valves in imaging systems.